Ethiopian foreign ministry spokesman said Tuesday that South Sudan's president "Salva Kiir" and rebel leader "Riek Machar" are flying for face-to-face peace talks in Ethiopia to try and end two weeks of fighting feared to have left thousands dead.

The world's youngest nation plunged into chaos on December 15 when Kiir accused his former deputy Machar of mounting a coup. Machar in turn has accused the president of using a clash between army units as a pretext to carry out a violent purge.

Regional leaders at the Inter-Governmental Authority on Development (IGAD), an East African grouping, have demanded Machar agree to a ceasefire and hold face-to-face talks with Kiir by Tuesday.

Ugandan President "Yoweri Museveni" has warned that Machar must comply with the ceasefire deal by Tuesday or face action by regional nations. He said if Machar does not respond "we shall have to go for him", without clarifying if his threat involved military action.